Crosspoints exist on the market which connect a plurality of N inputs to a plurality of m outputs, with each output being connected to a single input at most. Their usefulness arises from the need to connect source signals (video and audio, for example) to multiple loads (video monitors, for example), where the connectivity matrix can be conveniently reprogrammed via a digital interface.
Crosspoints exist which accept single-ended sources to produce single-ended outputs (single-ended-in single-ended-out), as well as crosspoints which accept their inputs from differential sources and produce differential outputs (differential-in differential-out). In the latter case, the differential inputs carry no useful common-mode (CM) information, so that the output common-mode is simply redefined and set equal to an arbitrary reference value.
In some cases the common mode voltages can be used to carry useful information such as control signals for horizontal and vertical control circuits for video information carried by the accompanying differential signal. One solution is to just construct larger crosspoint systems which can handle all of the differential signals and their accompanying common mode voltage so that they arrive simultaneously with the video carried by the differential signal. One shortcoming with that approach is that the voltage headroom is now more constrained by having to accommodate both the common mode voltage range and the differential signal range.